Ooh, I love YAF too! I've never been much for the SF/F, though. I loved historical, mystery, and animal books. Things like Encyclopedia Brown or the Young Indiana Jones Chronicles were some of my favorites. Lynne Reid Banks's I, Houdini is good for younger kids. It's a hamster's life told by the hamster who escapes from his house and has adventures. I also loved the Bunnicula books, too.

I may have to give some of the books you wrote about a try, especially Benny & Omar.

Here are the authors I've read and enjoyed from your list:
Zilpha Keatley Snyder- I adore the Eygpt Game, and have the Gypsy Game but need to read it.

E. L. Konigsberg- Of course, From The Mixed-Up Files of Mrs. Basil E. Frankweiler is one of my all-time favorites. Her other work is good. I have also read (George), which is very different and is about a boy who seems to have two personalities in his mind. But I want to read her other books as well.

Mildred C. Taylor- I read Roll of Thunder, Hear My Cry in middle school and didn't think I would like it at first. But it was very gripping and hard to put down! I think I finished it early because I enjoyed it so much. I think I still have it, too. Should give it a re-read.

Beverly Cleary- God, I loved her Ramona series when I was younger. They're funny, and being the younger sister, I could definitely relate.

I also like the stories of Edward Eager and E. Nesbit, although they may be for a slightly younger audience. I think Eager references Nesbit occasionally by having his children read her stories. The True Confessions of Charlotte Doyle is another I remember loving from that time period. I also read my first Agatha Christie in middle school (And Then There Were None), and I haven't stopped since. :D